1. Field of the Invention
This invention relates generally to methods for removing particulate matter and gases from a polluted gas stream, and more particularly to methods involving adding of electrostatically charged sorbent particles to a polluted gas stream containing particulate matter that becomes charged and adheres to the sorbent particles that are then removed, along with the sorbent reacted gaseous pollutants, in a series of moving beds of granular material with the removed materials recovered for use or disposal and the cleaned gas vented.
2. Prior Art
Only in recent years have air pollution control apparatus and methods been developed for the efficient and effective removal of fine particulate matter, particularly submicron particles produced in high volume processes. Earlier particulate removal methods and systems experienced substantial difficulties when they were required to meet strict requirements and regulations as have been imposed by governmental agencies for the removal of such particulate matter. Also, the removal of noxious gases has often present problems of a generation of non-disposable wastes as were produced in earlier industrial gas cleaning methods and systems.
Only recently have systems been implemented that overcome some of the above set out difficulties. Specifically, U.S. Patents to Schuff, U.S. Pat. Nos. 4,220,478 and 4,290,786, are directed, respectively, to a method and to an apparatus, for removing particulate matter from a gas stream that, like the present invention, involve injecting electrostatically charged particles of a sorbent material into a gas stream to form a large charged surface area to induce charging the particulate matter entrained in the gas stream. The charged particles contained in the gas stream together with the injected particles are passed through a porous moving bed of media of granular materials, wherein, as a result of the electrical charge on the particles and the inertial impact forces of the respective particles, the particles attach to the changing media. The media, together with attached sorbent additive and particulate matter are then separated for use in a product manufactured from which generated particulate matter or are disposed of, with the cleaned gas leaving the moving media for venting.
Like the earlier Schuff patents, the method of the present invention preferably utilizes an electrostatic charging gun for imparting a strong electrostatic charge onto sorbent particles introduced into the polluted gas stream. The sorbent particles all bear the same charge and thereby repel one another and are accordingly rapidly dispersed through the gas stream, creating a large charged surface area inducing charging of the particulate matter within that gas stream. This charged surface tends to agglomerate the submicron and larger particulates with the gaseous pollutants chemically reacted with the charged sorbent particles and with the media bed materials. The gas flow containing agglomerated particulates and sorbent particles with captured pollutants is then passed to moving media bed arrangements for the filtration and collection of the sorbent reaction product and particulates and gases from the gas stream, cleaning the gas stream that is then vented to atmosphere. The Schuff apparatus and method for its use, however, present limited capacity for particulate removal from high volume polluted gas flows. The present invention overcomes these deficiencies by including a practice of steps of the invention where the sorbent flow can be controlled and the electrostatic charging of the sorbent particles can be adjusted, and provides multiple moving beds of the same or different media material, each to present a large surface area of exposure to the gas flow containing sorbent reaction products and particulates, with the inclusion of a static bed for complete pollutant removal. Additionally, unique from the Schuff patents, the present invention the moving beds are contained within a housing that includes an airlock system that has a capability for maintaining the beds at a pressure less than atmospheric without the infusion of outside air, providing for a more efficient contaminant removal with the preferred system wherein the method of the invention is practiced being capable of operating at temperatures up to two thousand (2000) degrees F.